This invention relates to an improved mixing or agitating device, particularly to an apparatus for mixing viscous fluids and more particularly to an impeller having tubular blades which through the motion of its blades forces fluid into one part of the blades and out another part of the blades. This impeller is capable of not only imparting movement of fluid perpendicular to the length of the blade but simultaneously imparting superior movement of the fluid parallel to the length of the blade.
Many types of paddles, propellers, turbines and radial impellers and the like have been used to mix fluids. The fundamental problems of mixing and agitating of fluids are associated with the types of motion that can be imparted to the fluid. Mixing is the result of material transfer through momentum transfer and turbulence. Mixing requires moving the fluid, and is best accomplished by moving high velocity streams adjacent to low velocity streams creating flow velocity discontinuities. Whenever one fluid stream moves at high velocity compared to another stream, turbulence and agitation are produced, entraining adjacent fluid thereby producing the maximum mixing.
It is the shape of the impeller that determines the initial flow path, velocity and quantity of flow. The initial flow path depends on the type of impeller, such as marine-type propeller, turbine or flat paddle. The marine type propeller can produce essentially axial flow, i.e. flow that leaves the impeller in the direction of the axis of rotation or parallel with the shaft (the total flow path is determined not only by the impeller but by the shape of the container, the baffles or obstructions and the angle and place at which the shaft enters the fluid relative to the container). Flat paddles and turbines can produce essentially radial flow, i.e. flow that is initially parallel to the length of the impeller; perpendicular to the axis of rotation or shaft.
One of the most effective mixers for relative non-viscous fluids is described in U.S. Pat. No. 2,816,744 which was issued Dec. 17, 1957. The mixer of the above patent consists of a hollow tube with an entrance at its bottom with tubular blades attached to the hub. The tubular blades open into the hollow of the hub at one end and are open at the other end. The rotation of the impeller draws the fluid into the chamber of the hollow tube and jets it out the end of the blade thereby getting very good radial flow. In addition, the external portion of the blade is flattened at an inclination relative to the axis of rotation so that it acts as a screw type impeller imparting motion to the fluid essentially parallel to the axis of rotation.
There are many viscous fluids, such as drilling fluids, concrete, petroleum crudes, aqueous oleaginous emulsions and the like which are particularly hard to mix. Some of these fluids are prepared by blending liquids and dry granular ingredients, liquids and gases, or two or more substantially immiscible liquids. Many of the fluids tend to separate into layers, or to form thixotrophic gels. The mixing of viscous fluids such as dry and liquid materials, gels, thixotrophic gels and layered fluids is a difficult problem. The present invention is a mixer-agitator with an impeller which is able to mix viscous fluids of the above description, giving maximum radial or lateral flow, i.e. perpendicular to the axis of rotation. The impeller of this invention directly forces fluid into and through the tubular blades thereby achieving optimum lateral jetting action.